Radiative heat transfer coefficients for surface heating and cooling systems in indoor spaces considering radiatively participating gases
Lukas Schmitt, Martin Kriegel
Abstract
Designing surface heating and cooling systems in indoor spaces requires knowledge about the heat transfer between the surface and the room. Thereby, the convective heat transfer is already researched in detail for varying temperature differences, surface orientations and geometrical designs. The radiative heat transfer is still treated roughly in building physics, mostly assuming a non-participating medium, although the effect of radiation absorption is already proven to be significant in exemplary cases. Consequently, this paper aims for quantifying the energy balancing error for the entire range of typical and extreme boundary conditions in indoor spaces, if radiative heat transfer between surface and gas is ignored. Radiation exchange due to water vapor and carbon dioxide is evaluated by line-by-line calculations to define a separated radiative heat transfer coefficient due to radiation exchange between surface and gas. Thereby, the impact of radiation exchange between surface and gas to the total heat transfer at the surface is evaluated for varying surface sizes, orientations and temperatures as well as room sizes and air compositions. The impact of radiation heat exchange between surface and gas becomes most significant in case of high water vapor and carbon dioxide partial pressures, high surface temperatures, high indoor air temperatures and large rooms. In relation to the total heat transfer, radiation heat exchange between surface and gas has the greatest effect on the total heat transfer in the case of full-surface ceiling heating and floor cooling systems and should be considered in the design process.